Except that's not how it works.
Several research studies have been done on nutrition and breastfeeding, which is actually not true of many breastfeeding topics. They all pretty much show the same thing: your nutritional status, especially in the short term, has no impact on milk supply or the main components of what the milk is made up of. Not protein, carbohydrates, water, sugars, or calories. How can this be?
It seems that most women come out of pregnancy with a few extra pounds that they then use to produce milk. The body prioritizes milk-making over adding weight or nutritional stores into mom's body. And here's where the advice gets confusing.
THERE IS A DIFFERENCE BETWEEN SOMETHING BEING GOOD FOR YOU AND IT HELPING YOU MAKE MILK.
You eat and drink well in the postpartum period for YOU. You need to replace the vitamins and minerals you used during pregnancy. You need to not be hungry or thirsty on top of everything else that comes with a new baby. Not everything is about those ounces in the bottle.
My solution is soooo boring. Eat healthy. That's it. But not to increase your milk supply. Because YOU need to replace all the nutrients you are now low on. Another good effect of eating healthy is that your baby gets healthier milk. Don't get me wrong, milk from a mother with the crappiest diet is still much better that artificial milk, but it's just a fact that when mom eats healthy, so does her little one.
There are a few things that when increased in mother's diet also increased in the milk. It seems the amount of fatty acids in the mother's diet greatly impacts the fatty acids that will be in her milk. We want the kinds of fats found in natural foods like nuts, avocados, seafood. The unhealthy kinds of fats are high in prepared and snack foods, and they can drastically decrease the amount of fat in milk. The study linked to above says, "Fat is considered one of the most important nutrients of human milk and is used to provide energy for the breastfed infant. Among studies conducted on the FA composition of maternal diet and breast milk, observational studies mostly demonstrated a positive association of FA composition, including DHA, LA, oleic acid, EPA, and PUFA, in maternal diet and, subsequently, in breast milk. Moreover, several clinical trials found a significant improvement in fat-soluble vitamins and fat content of breast milk after maternal supplementation."
Other things that are changed depending on mom's diet are: vitamins A, B12, C, D, and the minerals calcium, copper, lead, and choline.
Protein quality also seems to improve the quality of milk by increasing the amount of whey, which is very digestible. Good-quality protein mostly come from animal products, so vegetarian moms need to be especially careful.
Fish was another really easy way to improve the awesome fatty acids in your milk. It was not found to increase mercury levels in milk, as some people thought might be the case. Thank you, scientist people and statistical nerdy-types for doing this kind of research and finding that fish is not only safe, but really good for breastfeeding women.
If you really need to make more milk then let's talk about the things that will actually help you reach that goal. There's plenty of them. Increased and more efficient nursing or pumping being the most important. That's a whole other topic. Find an IBCLC and work on finding out if your supply is actually low and what to do about it. Herbs can be of some benefit for some women in some situations, but you need to find someone who actually knows the proper dosages and which ones would be best. Don't drink a cup of random tea with a teaspoon of herbs and think you've done anything. As an Herbalist, I find the doses most women are told to take to be ridiculous.
And this is where I have a beef with all the lactation cookie talk. The ingredients in lactation cookies will do zippo for your milk supply. They are usually healthy ingredients with lots of good fats that will in turn will raise the levels in your milk, but they don't make you make more of it! Not to mention all the extra sugar they add to your diet that is not helpful. It's just so sad how much money women are spending on foods that don't do what they want them to.
Why not spend a little less money on lactation cookies and lactation teas, and more on fresh fruits and vegetables? Cook them well and add some butter or olive oil to help you absorb all the nutrients you can. Eat when you're hungry, drink when you're thirsty, and relax about needing to stuff yourself in order to breastfeed.